The present invention relates to aquaculture systems for commercially raising fish, particularly crustaceans including, but not limited to, crayfish, crabs, lobster and shrimp.
In recent years the world has witnessed an alarming decline in commercial fisheries, the result of over fishing and environmental degradation. Over the years, many of the traditional sources for fish, i.e. lakes, rivers, streams, etc., have become contaminated with pollutants generated by the public. As a result, fewer fish are available in such sources; and, in addition, fish that are able to survive in the contaminated waters often themselves become contaminated and unfit for human consumption. According to the Food and Agriculture Organization (FAO) of the United Nations, nearly 70% of the world's commercial marine fisheries species are now fully exploited, overexploited or depleted. Based on anticipated population growth, it is estimated that the world's demand for seafood will double by the year 2025. Therefore, a growing gap is developing between demand and supply of fisheries products, which results in a growing seafood deficit. Even the most favorable estimates project that in the year 2025 the global demand for seafood will be twice as much as the commercial fisheries harvest.
It is very clear that the only way to meet the world's growing needs in fisheries products is through marine aquaculture systems—the farming of aquatic organisms in controlled environments. In response to the situation, global aquaculture production is expanding quickly. Aquaculture's contribution to the world's seafood supplies increased from 12 to 19% between 1984 and 1994. Worldwide, it is estimated that in order to close the increasing gap between demand and supply of aquatic products, aquaculture will need to increase production three-to-four-fold during the next two and a half decades. In this context, there is a compelling motivation to develop aquaculture systems of improved and commercially viable character for high volume production of aquatic species and environmental sustainability.
In an effort to eliminate the effects of marine aquaculture on the environment, and to optimize aquaculture production, an environmentally acceptable aquatic farming technology has emerged: the use of recirculated marine aquaculture systems (RMAS), in which the same water is continuously reused in operation of the system. These systems have many advantages over non-recirculating systems which typically require periodic water exchanges. There are drawbacks to periodic water exchanges; namely, additional water usage, waste material generation that may be adverse to the environment, and an increased cause of stress to the cultured aquatic species. Water re-use in the RMAS minimizes any adverse environmental burden created by the aquaculture system since there is minimal net waste material generation, and what waste is generated is easily handled by local sewer systems, or can be used as fertilizer. RMAS offer flexibility in location options including urban, rural, and inland, since they are not confined to coastal areas or open oceans. Unlike free-floating pens, process conditions can be better controlled within a RMAS. In addition, RMAS minimizes the stress caused to the cultured aquatic species by management of the waste material generation (carbon dioxide, protein, nitrates, nitrites, etc.) and preservation of the floc of beneficial bacteria without breaking the floc. Systems that break the floc of beneficial bacteria must be given additional time and fine tuning to create an effective relative proportion of beneficial bacteria to water.
RMAS typically includes a container containing a large quantity of water in which the fish are raised, and a filtration system for cleaning the water in the container. Such filtration systems typically include a particulate filter and a bio-filter. The particulate filter is used to remove solid particulate materials, such as fish waste and uneaten food, from the water. The bio-filter contains bacteria which removes ammonia and nitrates from the water, and also is used to oxygenate the water. Various types of filters have been used as particulate filters in aquaculture, including rotating drum filters. The use of rotating drum filters in aquaculture, however, has been limited by their high cost, their need for frequent maintenance, and the difficulty in cleaning the filtering surface of the filtering media. The filtering surface must be continuously cleaned to prevent the filtering surface from being clogged by the particulate matter.
In general, aquaculture systems of the prior art are not well designed for use in connection with crustaceans. As a result, the commercial aquaculture systems developed to date are highly variable in efficiency and output of product. Such systems are subject to numerous processing and operational deficiencies, including: sub-optimal production of fish; absence of control of process conditions; process instability; susceptibility to environmental pathogens; susceptibility to pollution; loss of stock; and the lack of well-defined optimal conditions for achieving maximal growth and production of the aquatic species being raised in the aquaculture system.
Despite the various features and benefits of the structures of the prior aquaculture systems, there remains a need for a recirculated marine aquaculture system and process that is specifically designed for crustaceans, including, but not limited to, crayfish, crabs, lobster and shrimp. There remains a specific need for a low-cost system that can grow crustaceans from an early post larval stage to a market ready stage at a well defined time interval that can be repeatedly cycled for optimum return on the system investment.